


Let's break some boundaries

by Bleach_ed_Na_tsu



Category: Katekyou Hitman Reborn!
Genre: AU, Adult!R27, Adult!Reborn - Freeform, Alternate Universe, Gen, M/M
Language: English
Status: Completed
Published: 2020-03-20
Updated: 2020-03-20
Packaged: 2021-02-28 17:01:14
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,761
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23230612
Author URL: https://archiveofourown.org/users/Bleach_ed_Na_tsu/pseuds/Bleach_ed_Na_tsu
Summary: Reborn was finally free of the curse and adjusting to being full-grown once again while Tsuna is faced with visions and emotions trickling back from the future and with it realises exactly how important his tutor has come to be to him; even if those feeling scare Tsuna more than going to the future did. Adult!R27. Birthday fic for Icyvampire123.
Relationships: Reborn/Sawada Tsunayoshi
Comments: 4
Kudos: 205





	Let's break some boundaries

To hear that he wasn't going to die, that he was going to be an adult again, and that he'd stay with Tsuna and not leave him did horribly wonderful, terrible things to Tsuna's insides. Part of the young man was terrified. If Reborn didn't leave then his 'normal' life would never return, but that part was so small and insignificant by now that it almost was not there. He accepted his title long ago, after the Shimon incident when he realised that the power needed and the ability to protect those he cared for came with the title of Decimo. Another part of Tsuna was giddy, excited, and nervous. His insides tumbled and writhed, and he wasn't really sure why. Sure, it could be because Reborn is a _Hitman_ and surely that isn't someone you want in your house with your innocent mother and the three children who –were part of the mafia, yes- but were also incredibly important to you even if you wouldn't admit it.

Tsuna knew that wasn't the reason though, he had long ago looked past Reborn's title and instead looked at the man trapped in the child's body. It made him giddy with anticipation to see the man's full form, to see exactly how strong Reborn was, how willing, and how handsome.

These thoughts scared Tsuna, of course they did. He did not want to admit to not liking Kyoko anymore, never mind liking men, and he wanted to admit even less to liking one particular man. After the future incident, having to deal with the finer points of emotional stresses and fatigue, and finally _looking_ at both Haru and Kyoko, Tsuna had figured out that neither girl was what he wanted. They were close to him; he would openly admit that they were precious to him, but in the same way that Lambo, Fuuta, and I-pin or any one of his guardians were precious to him. His life would not be full without them and he would lack reason to live. But his love, and those he was destined to love, he found out later, were not any but one man.

But Tsuna had learnt that the hard way. Learnt the fear, the straightforward terror and loss he felt when he went to a future where Reborn was not there. The sheer gut-clenching horror of being told that his tutor had been killed; first it was disbelief and nervous scoffing, then the pure blinding pain set in his chest and only when he was back in the base and saw his tutor- infant or not- did that burn finally disappear and settle into something new and undiscovered. When he was lost in the woods alone with an inexperienced, fool-hardy Gokudera, and even before that when the pink smoke didn't reveal his Tutor from the future Tsuna realised something dark and new about himself, and about the feelings he held for his tutor.

Tsuna watched as the Arcobaleno celebrated and the gathered masses went away to heal, then and there, watching the completely unguarded joy in Reborn and the other Arcobaleno's faces, Tsuna decided that he really needed to change if the future wasn't to happen again.

* * *

There was a rough shaking at his side, and when he rolled over to see who it was Tsuna was surprised to see that it was his tutor waking him. "Dame-Tsuna, wake up. We have training later today."

Sitting up Tsuna noticed that his tutor had aged again and today was the image of a twenty-one year old man- just three years older than Tsuna now.

Everyone was surprised when they realised that the Arcobaleno were not aging as normal people aged. Slowly the group of the strongest were jumping years in the space of weeks. Sometimes only a year would pass by the week's end, and sometimes three or four would pass in days. In the beginning Colonello jumped ten years in the space of two weeks and later that week jumped another five. By then- being physically 25- he had proposed and proceeded to officially marry Lal in a ceremony that had everyone teary and happy. Then he slowed down drastically, finally reaching Lal's age of 28 and hadn't aged since.

"Did you have another growth-spurt, Reborn?" Tsuna yawned as he changed.

Yesterday Reborn had been fifteen, and that had been a gradual aging over the course of the month. Reborn seemed to have routine growth spurts every month where he would jump between four and six years. This time it seemed that the jump was much larger, which would meant that Reborn was coming to the end of his rapid growth- if the pattern held from the other Arcobaleno.

Reborn made a non-committal grunt and moved out of the room with an over the shoulder wave telling Tsuna to be downstairs before his food was gone.

Tsuna sighed and rubbed his head, trying to rid his mind of the nightmare that plagued him that night. Though luckily it had been a while since the last one and he had learnt to control his outward reactions to the images.

Since the future incident Tsuna had grown quickly, and through the growing had nightmares. Trinisette did well to protect its bearers from trans-dimensional and past mistakes. Uni and Byakuran received clear images of the various effects their actions would take, but Tsuna did not, instead his mind was ravaged by nightmares that altered the way he thought and acted. He learnt of the mistakes he made by not accepting what Reborn was giving him.

It helped him of course, the pain and grief, because he had broken the curse of the Arcobaleno- with everyone's help- and that was something that hadn't happened before.

Yawning he made his way downstairs. "Morning, mom." He greeted.

It wouldn't be long till he was out of the house, in the next few months it was planned for him to move into the Vongola mansion to begin the inheritance ceremony again and start the transition to boss-hood once he had a little more personal time with his guardians being eighteen.

"Good morning, Tsuna-nii." The three mafia children greeted him as he took his seat across from Reborn and he smiled and greeted them each in tandem.

It was hard to believe that Fuuta was almost fourteen and that I-pin and Lambo were almost nine. All three were doing well in school and had very little to do with the mafia besides training and the occasional ranking Fuuta sold for a little extra money. They had all promised Tsuna to finish school before deciding what to do with their future; joining Tsuna or not. He had been adamant that he did not expect them to join him but that they would be welcomed regardless of their rank, position, or choice. _"You will always be my Family, even if you aren't in my Famiglia."_

"Morning." He began his breakfast only to have some of his rice stolen by Reborn. "Oi, Reborn! Don't you think that you should let a growing boy eat!?"

"I'm growing too, Dame-Tsuna."

Tsuna had to pause as he watched Reborn smirk and sip at his coffee. The man's face was sculpted and sharp. His nose was slightly pointed and his lashes long. The curve of his eyebrows were neat and soft and the way his lips lifted to smirk- and rarely smile- made Tsuna's stomach drop in anticipation. But he found he loved the dropping sensation and the dark, heavy emotions that filled his stomach as it did.

Tsuna gulped and tried to hide his blush behind his bowl of rice- or what was left of it. He didn't have the leeway to afford to watch Reborn like that. His nightmare still plagued him and the snippets of images still burned through him.

Lust or not, Tsuna couldn't afford to let himself fall for Reborn, not when the future was not set in stone. Not when he could still lose the man.

* * *

_Flashes scorch behind his eyes as he is cast back into one of the nightmares that filtered from the future. It's a scene he has seen too many times to count now, the reaper and reminder that he failed once and ought not to fail again._

_Reborn lies on his bed pale, sickly, but fighting._

_Always fighting._

_Tsuna enters the room and sits at the bedside holding one weak, pale hand in his own wider ones. There was something wrong with the image of him being stronger and sturdier than Reborn, the man was his rock and was his everything; here he was fading before Tsuna's eyes._

_The man was sleeping, he had been for days. There was no life to his chest, even if it moved, and there was no colour to his cheeks. Even his hair seemed limp._

_But Reborn kept fighting._

_Leon has died weeks ago, sickly and pale she couldn't live off of the dwindling flames of her master any longer and succumbed to the long slumber that death offered her. Tsuna had never seen Reborn so broken. Leon was everything because he had followed Reborn through everything- the curse, the tutoring, the growth, the Non-trinisette. Everything._

" _I'm going to save you, Reborn. I won't let you die like this." Tsuna practically wheezed, because he was hurting just as much to watch the only man he_ truly _respected die before him. He couldn't even do anything about it!_

" _Don't try to save a lost cause, Dame-Tsuna." Reborn had coughed out with breathless force, "I am going to die a dog's death; I always knew I would curse or no curse."_

 _Tsuna didn't care that it was week, he bawled his eyes out in the hospital room when Reborn divulged that to him, because he_ knew _he couldn't save his ex-tutor now something else. Tsuna_ knew _it and it was devastating._

_It was the next day that Reborn died, Tsuna had been forced to leave the safety of the base to fight for the lives of the Namimori civilians as Millfiore bore down and painted the world red with insanity._

_No one, not one of the guardians understood the sheer devastation and horror that stuck and broke Tsuna when he arrived back to hear that Reborn- the last Arcobaleno- had finally succumbed to the poison of Non-7^3. Except maybe Hibari Kyouya._

_Hibari was the only one who knew what made Tsuna decide to go ahead with his radical plan to call forward his fourteen-year-old self and his guardians to the future._

_Reborn's death was only two days before his own at the hands of Byakuran._

_Tsuna arrived exactly four days after Reborn's death in the future and changed his future exactly four months to the date._

Sitting up suddenly a cold rush lances through Tsuna's spine as the coolness of the night filters into his perspective. He never did sleep right with Reborn moved out of his room.

Tsuna lets his head roll back to stare at the ceiling, hot tears cascade silently down his face and he makes no move to stop them. He is tired, and he is hurt. But the burning he feels has little to do with the tears eroding at his pale cheeks.

He knows why he burns when he sees Reborn die alone in the future. He knows why hot flushes flash through his core when Reborn smiles at him. He understands why his tutor is not longer just that.

He loves reborn with his whole heart, and it took losing him to his own Dame-ness to finally realise it.

It only meant that Tsuna couldn't have him, because he knew- innately, from his nightmares of a certainly changing future- that he could not handle losing him again.

* * *

"Tsu~ are you sure you'll be okay home alone? You haven't been looking yourself lately." Nana worried over her teenage son. Though he had grown and matured delightfully over the years she would always see the brunet as her little baby boy that tripped on air.

"I'll be fine Okaa-san. Reborn's here anyway. So I'm not alone." Tsuna smiled and kissed his mother on the cheek before ruffling the kid's hair and sending them off.

He was always bemused by his mother's antics. He was almost nineteen, about to move out, and his mother still treated him like the young teen he was that couldn't hold a conversation and was getting sub-standard grades in school. Though, Tsuna wouldn't change it for the world. He loved his mother, and she was still a large part of his world, even if that world had gotten much larger since his younger years.

"Okay, bye Tsu~"

"Bye, bye Tsuna-nii!"

Tsuna waved as his family left. He had worked out to buy them a little vacation to a hot spring not too far away, it had been a little expensive, but considering all he owed his mother, and how he loved his siblings, the little expense was nothing- especially when compared to the utter surprise and excitement that lit his mother's face when he gave her the gift for her birthday. He had even ordered Lambo's favourite Cyprian grape-candy, Fuuta's favourite brand fountain pen, and a new set of martial-arts robes with her name embroidered into the cuff for I-pins graduation ceremony in a month.

That left Tsuna and Reborn alone in the house, it suited Tsuna perfectly, but it meant he had to hide his almost blatant lust for the man and had to try and not catch sight of him half-naked leaving the bathroom after a shower. It had happened too many times before for Tsuna to count. It was like the man did it on purpose.

Sighing, Tsuna moved to do some chores around the house. It wasn't particularly dirty, but since training was canceled for the day and he had nothing else to do, Tsuna needed something to keep his hands busy.

Tsuna was sweeping the hall when arms wove around his waist in that eased way of a man with confidence. They squeezed with a force that bordered on painful and hot breathe stroked passed his ear. Tsuna leant back instinctively, and caught himself when he realised what he was doing.

Hot breathe coiled around Tsuna's neck and brushed in a tickling, soft way. The chest pressed against his back rumbled with a purr that seemed to shake Tsuna's entire body and warmed something private in his core.

Reborn mumbled soft nothings into his neck, and each and every syllable was possessive, strong, and self assured. Tsuna wanted nothing more than to fall back into the arms. To fall into the words; to rest everything on Reborn's shoulders, even if only for a minute.

Then a flash boomed behind his eyes and Tsuna saw all the memories from the future, and some of the memories that the Trinisette filtered into his mind of the turmoil his future self suffered at the death- and previously suffering- of the Arcobaleno, but specifically of Reborn. It scorched through Tsuna and made him stiffen in a very physical way that alerted Reborn to his student's turmoil.

Reborn stopped his ministrations of affection and instead loosened his grip enough to be less desperate and more comforting. He peered over Tsuna's shoulder, trying to gauge what exactly made his student- who he would _bet_ was enjoying the attention- freeze and shake so suddenly and aggressively. To Reborn, it seemed like Tsuna was terrified of something.

"Tsuna," Reborn hummed, the brim of his fedora crumpling against the back of Tsuna's head. "What's wrong koi?"

"Reborn, let go." It hurt to say the words; it hurt because he didn't want to. He didn't want to be let go, for Reborn to remove himself from his side. Tsuna didn't want to let go of Reborn. The Hitman knew it too.

Tsuna was suddenly turned around to face the darkened eyes of the Hitman that changed his life. His hands were pinned above his head in one large hand of Reborn; the other was fiddling with the hem of Tsuna's dark dress shirt. There was challenge and hurt in his eyes, there was confusion, and a glint of knowing; Reborn knew Tsuna was lying to himself.

"I won't let go of something that is mine, Dame-Tsuna." He purred, his voice dark and dangerous, there was no room for debate, and the warm breathe scented with tobacco and peppermint practically melted Tsuna. "Why don't you stop lying to yourself Tsuna? You are mine."

Tsuna tore his eyes away, he was ashamed. Here was Reborn, offering him everything he wanted, everything he yearned for, and he was too much of a coward to take it. "I'm not worth it." His words were soft, whispered on lost breathe as tears touched his lashes.

Reborn froze, his lips halting just before Tsuna's ear, he had been planning to make the teen blush scarlet, but he hadn't expected his student- soon to be ex-student- to say such words. Especially not in a tone of voice that left Reborn bristling. Tsuna seemed so broken.

"Tsuna, what aren't you telling me?" Reborn was genuinely worried beneath his bravado. His tone may have been thick with that seriousness and harsh bite, but of anyone he knew his student would be able to read through that bite.

It was the strangest thing for the Hitman. Never, not when he cared for Uni, not after all the eternal time with the Arcobaleno, had someone been able to manipulate him in the way Tsuna could. Never had Reborn leant on anyone but himself, and never had anyone been able to read the subtle inflections and minute changes in his tone, timbre, and words. Tsuna could. It scared the Hitman sometimes, because Tsuna was 'Dame'; he was not too intellectual, and he wasn't –at first- strong. But he was ever so encompassing, he could make anyone his friend and ally. He could make anyone his lover or his mate. He could have anyone. Yet here he was, wanting Reborn. And reborn knew that Tsuna wanted him, had seen the lust and the confusion in golden-chocolate eyes as they raked his form when he boy thought the Hitman wasn't looking. Those sheer lusting, compassionate looks never failed to bristle through Reborn in the right way. Reborn wanted them for himself, even if he had to force Tsuna's hand right now.

Reborn was a man of many faces and many words. He lived in both day and night, he killed and he rescued. He was handsome, suave, and he was a gentleman where gentlemanly fashion was due. He could have anyone. He could walk into a bar and be dripping with men and women alike within a moment's notice.

And here he was being drawn into and subdued by a boy in his late teen with innocent eyes and skin as soft and pale as spider-silk and snow.

It was a strange feeling, that lack of control. Reborn prided himself on his emotional rein, and here he was completely loosing it because this boy, the one he loved, was in turmoil over something he didn't understand.

"Koi, what is the matter?" he went to stroke Tsuna's face with one hand when the boy slapped his hand away. His eyes were brimmed with tears and a shattering frown marred his face.

"I lost your once Reborn, because I was Dame, I leant on you and I didn't think about the consequences my actions would have on those important to me!" Tsuna cried as Reborn re-pinned him to the wall. Reborn's hands were the only things keeping Tsuna on his feet, because his legs certainly weren't doing their job at this point. "I don't want you close to me, only to find out again that I'm not strong enough to protect you!"

Reborn stood stalk still for only a flicker of a moment. His eyes widened as he watched trails of liquid crystal track the cheeks of the boy he would have once called a useless waste of his time. But that was a long time ago. Equally, it had been a _long_ time since someone cared enough for Reborn to get upset about the prospect of his getting injured, let alone dying. It was humbling in a way, and it filled Reborn with a kind of deep, wonderfully-awful warmth that infected and softened him; even if he wouldn't admit it to anyone but himself- and maybe Tsuna one day. Releasing Tsuna's hands, wrapping his arms around the slim waist instead to keep the quivering boy standing, Reborn stroked Tsuna's face with his free hand and let a soft smirk- one bordering on a genuine, warm smile- lift his thinned lips as Tsuna unconsciously tussled into his callous hand.

"When have I ever needed your protection, Dame-Tsuna? I was at fault for letting myself die, you were not at fault." Reborn was soft, because he may be a Hitman, he may kill and torture for a living, but he was a man- a _gentleman_ he would insist- and when something that was his was hurting and broken it was his job to fix it. Tsuna made him a protective beast and he didn't feel like that would change any time soon.

Reborn had seen the future. Everyone involved had gotten the memories of their time in the future, but a select few – those involved with the Trinisette- received memories in the form of nightmares from their future selves. Nothing explicit, but enough to set even Reborn's teeth on edge as he learnt of the weight of Non-trinisette. His life- and death- in the future was gruesome and agonising, it was horrendous to think of what _Tsuna_ was seeing, because Reborn could only see so much, was only given so much by the Trinisette; after all he died before the time where Tsuna really started to grow up and before the –for lack of a better term- shit hit the fan.

Reborn could understand why Tsuna- compassionate, fragile, inherently loyal and protective Tsuna- was so broken by the images he was subjected to seeing of a future he had a hand in creating. Reborn knew of the nightmares, and at one point he had thought about moving back in with the young brunet boy. But there was little he could truly do for nightmares, the one thing he could do was create memories overwhelm the boy's mind and promise to irradiate any nightmares in a fuel of lust and waves of hormones.

Lips crashed together before Tsuna could react.

Fiery touches lanced over Tsuna's skin, and if it weren't for the fact that his mind- only momentarily ago- was blasted with grief, turmoil and distress then suddenly pleasure and sinful thoughts, he would have been upset about the buttons flying across the room. He was wearing a new shirt.

For all the touches and bites Reborn was marking him with, his touches and the glances he threw at Tsuna when his mouth was not somewhere it should be, were all devastatingly soft. Tsuna was being driven mad!

Touches roamed his entire torso, they fiddled with what was left with his shirt, and they teased and tickled the skin of his ribs and of his chest. Large hands grabbed his hips in a tight hold as a mouth, so hot and bruising descended on his own.

Before Tsuna even realised it his own arms were pulling Reborn in, he was sliding up the wall as his legs pulled him into Reborn's hips and Reborn pushed his back into the wall of the empty hallway. Tsuna moaned, he was confused, in pain, and still filled with the fear of losing Reborn if he leaned to heavily on the man he respected, and would openly say now- with a hundred thousand emotions writhing in his heart- that he loved.

Reborn pulled away from Tsuna's mouth for a moment. His eyes flickered to the darkening bruises that decorated Tsuna's lithe form from his neck to his navel. He smirked; because Tsuna was a work of art and was suitably claimed. Then his eyes roamed to his panting love's face. It was flushed with arousal and possibly embarrassment, there were still tears leaking out of Tsuna's golden-brown eyes, but they were substantially less ferocious in their trails.

Kissing away the tears, savouring and despising the taste of sweetness to them, Reborn pressed his forehead to Tsuna's. His fedora was long gone, cast away when Tsuna's wild arms had wrapped around his neck.

"I promise you Tsuna, I will not let myself leave you. You can lean on my all you want, I will _never_ let myself be taken from you again." This time his words were strong, they were tensed and sturdy, and Tsuna despite his fears and pains fell into their truth almost immediately. They had both learned from their trip to the future what lay ahead and what they needed to change. What they had to lose if they didn't. It was a lesson worth the turmoil, grief, and terror of fighting enemies too far advanced for them. It was worth the nightmares, and it was worth the growing pains that plagued both Tsuna's mind and body as he tried to put himself into a position that up until only a few years ago he was not ready to fulfil.

"How can you promise me that, Reborn?" Tsuna was folding, Reborn could hear it in the tired, relieved tone and the softness of the embrace Tsuna had around his neck and hips.

"I promise it with my dying will. I am the greatest Hitman after all."

When Tsuna's reply was but a soft nod and the warmest smile Reborn had seen on the boy's lips since the entire Bermuda fiasco, Reborn could only smirk and sear himself into Tsuna's mind with another bruising kiss and wicked hands breaking all the boundaries that were between them away from the aroused, connected pair.

* * *

Tsuna breathed softly on Reborn's bare chest, his grip on the scarred waist was relaxed but possessive and Reborn purred as Tsuna's pale fingers brushed comfortable, innocent patterns along his toned stomach and the skin stretched across his narrow hip-bones. In turn Reborn stroked his fingers comfortingly up and down Tsuna's spine; his other hand cradled the cigarette that let its smoke coil slowly through the air before disappearing into the night through Tsuna's open bedroom window.

It was a habit both he and Tsuna despised, but, Tsuna would guiltily admit that the smell of faded tobacco and nicotine, mixed with Reborn's own cologne and the strong toothpaste he used to fade the scent were comforting and filled Tsuna with some kind of warmth and security. It was a guilt confession, because the smell came at the price of –possibly in the future- Reborn's health.

Both men were sweaty but contented, it smelt like love in the room and though Tsuna was still brilliantly embarrassed, he couldn't find it in himself to regret it. Something had clicked in them both that evening, it balanced them somehow when they were crying out each other's name, Tsuna knew it because his mind no longer faltered and had rushes of panic and unease, Reborn knew it because what was his was finally _his_.

Tsuna sighed contentedly, "I love you, Reborn." Though during their love making Tsuna had practically screamed his name in ecstasy more times than Reborn could count- and had confessed his love tenfold- those same words spoken in fatigue with that hint of lust still lingering in the tone made Reborn fill with a heavy, dark emotion that left his resolve flaring and roaring. He never imagined hearing the confession- the confirmation of his love's affection -would affect him so much.

His hand stopped in its lazy trail and instead Reborn tightened his grip on Tsuna's form. His eyes trained the lithe, sweaty body and lingered on the light scratches that littered Tsuna's skin from his nails and the darkening claim marks from his teeth and tongue. There was something satisfying about hurting Tsuna in a way that made the boy blush and call out in bliss. But there was a promise in those wounds. One Reborn was never likely to forget, nor break.

"I love you, Dame-Tsuna," And just as Tsuna nodded off, happy to feel his love in his arms and next to him in bed, he heard Reborn's husk, emotional voice beside his ear as a kiss dropped onto his forehead. "and you'll never fight alone again."


End file.
